For a coral, the more housekeepers the better

Sedimentation is a constant problem for certain corals depending on their location on the reef. If there is too much sediment buildup within a coral, it can get buried and die. However, if it hosts enough symbionts, they can help remove a significant amount of sediment in their nightly activities.

A close up of a coral with both Trapezia serenei (top) and Alpheus lottini (bottom). Photo

We've seen how Fungiid corals can inflate and deflate themselves in order to combat sedimentation. However, other corals aren't as lucky as these Fungiids and they need help from outside sources.

Stier, Gil, and McKeon performed their study on the island Moorea in French Polynesia on its western shore. There they removed heads of similarly sized Pocillopora sp. coral from the reef and transferred it to their testing facility nearby. Prior to testing, all of the commensal shrimps, crabs, and fish were removed from the corals and saved for later sediment removal potential.

What the researchers found was that by themselves, Pocillopora sp. corals can remove at most a 10% sedimentation level. However, with two and four commensal organisms present, the sediment removal increased from 30% to 48% respectively. The mode by which the sedimentation was removed remained unclear to the researchers:

This may be the focus of future work to better understand how the sediment was being removed.

That being said, they positively correlated increased sediment removal with total number of symbionts within the coral. As the coral continues to grow, it should continue to support more and more crab and shrimp symbionts in order to help with sediment removal.

Incidentally I also covered how these same shrimps and crabs fend off attacks by seastars so they are performing double-duty for the corals as well.